Ultrastructure of transrectal coelomoducts in the sea cucumber Parastichopus californicus (Echinodermata,Holothuroida)

Summary The perivisceral coelom of the sea cucumber Parastichopus californicus is connected to the lumen of the hindgut by as many as 200 short transrectal ducts. Each duct is lined by a pseudostratified epithelium composed of: (i) monociliated, tonofilament-containing cells, (ii) myoepithelial cells, (iii) bundles of neurites, and (iv) granule-containing cells. In most places the lumen of each duct is lined by the monociliated, tonofilament-containing cells. The myoepithelial cells are predominantly basal in position and circular in orientation, but some border the lumen and parallel the long axis of the duct. The epithelium of a duct consists of the same types of cells as occur in the peritoneum covering the rectum and differs markedly from the nonciliated, cuticularized epithelium that lines the lumen of the rectum. Based on ultrastructural characteristics, the transrectal ducts represent evaginations of the peritoneum overlying the rectum and are thus coelomoducts sensu Goodrich. The possibility is discussed that perivisceral coelomoducts of holothuroids function in regulating coelomic volumes.Abbreviations AE adluminal epithelium - AF anal fold - ANC anal coelom - AS anal sphincter muscle - B bacterium - BL basal lamina - BW body wall - CC coelomocyte - CI cilium - CO collagen fibers - CT connective tissue - CTE ciliated, tonofilament-containing epithelial cell - D desmosome-like junction - FB fibroblast - GB Golgi bodies - GC axon-like process of granule-containing cell - HD hemidesmosome - IJ intermediate junction - INT intestine - LM longitudinal muscles of body wall - LRW luminal surface of rectal wall - ME myoepithelial cell - ML microlamellae - MY myelin-like material - NE neurite - NV nerve - NU nucleus - OI opening of intestine into rectum - PC perivisceral coelom - PT peritoneum - PTF papilliform tube feet - RW rectal wall - RL rectal lumen - RS rectal suspensor - RT respiratory trees - SJ septate junction - SO soma of adluminal epithelial cell - SM subepidermal muscle - TD transrectal duct - TF tonofilaments - WVC lateral water vascular canals     

Ultrastructure of the Statocysts in the Apodous Sea Cucumber Leptosynapta inhaerens (Holothuroidea, Echinodermata)

The burrowing sea cucumber Leptosynapta inhaerens possesses five pairs of statocysts, one pair on either side of each radial nerve cord where it arises from the circumoral nerve ring. The nerve cords exhibit only ectoneural components at the level of the statocysts. A sinus-like epineural canal lies superjacent to each cord. This canal is lined by a robust monociliated neuroepithelium which lacks any special support cells. Beneath the neuroepithelium, the somata of the ectoneural neurons form a perikaryal layer whereas the axons are located within the proximal parts of the cords. Glial cells have not been found. Each statocyst is a hollow sense organ. Its central cavity is lined by a monolayer of monociliated parietal cells. Axons of these parietal cells extend towards the statocyst nerve which connects each statocyst with the ectoneural pathways of the cord. A single lithocyte floats within each central statocyst cavity. This unciliated cell contains a voluminous vacuole with the statolith and several smaller vacuoles. It is concluded that statocysts do not belong to the basic organization of the Holothuroidea but have been evolved within this group. The statement, that the statocysts of apodous sea cucumbers and that of the enigmatic Xenoturbella bocki are homologous organs, is rejected.     

Parallelisms in the evolution of sea cucumbers (Echinodermata: Holothuroidea)

The importance of taking into account parallelisms in the evolution of morphological characters is analyzed for the taxonomy of the class Holothuroidea. The establishment of the order Dactylochirotida and classification of the order Elasipodida serve as examples to illustrate insufficient appreciation of parallelisms in Holothuroidea. The following characters, evolving independently in different groups of sea cucumbers, are considered: a stout skeleton, reduction of the calcareous ring and the body wall sclerites; similarity of body shape; similarity in the shape of tentacles; reduction in the number of tentacles from 12 to 10 in different fam-ilies and subfamilies of the order Synaptida. Based on the analysis of morphological and molecular data, the family Deimatidae is transferred from the order Elasipodida to the order Aspidochirotida. It is hypothesized that the concave cup-shaped sclerites with three to five rays occurring in the family Laetmogonidae (order Elasipodida) are of paedomorphic origin and correspond to the early growth stages of the laetmogonid wheels; the concave cross-shaped sclerites of the families Elpidiidae and Psychropotidae may have originated from laetmogonid concave cup-shaped sclerites. Emended diagnosis of the order Elasipodida is proposed. The family Vaneyellidae previously synonymized by the author with the family Cucumariidae is reestablished, and its emended diagnosis is also proposed.     

Phylogeny of Holothuroidea (Echinodermata) inferred from morphology

Holothuroids, or sea cucumbers, are an abundant and diverse group of echinoderms with over 1400 species occurring from the intertidal to the deepest oceanic trenches. In this study, we report the first phylogeny of this class, based on a cladistic analysis of 47 morphological characters. We introduce several previously unconsidered synapomorphic characters, examine the relationships between representatives from all extant families and assess the assumptions of monophyly for each order and subclass. Maximum-parsimony analyses using three rooting methods recovered well-supported and identical topologies when two small and apparently derived families, Eupyrgidae and Ge-phyrothuriidae, were removed. The results suggest that the higher-level arrangement of Holothuroidea warrants a considerable revision. Apodida was sister to the other holothuroids. The monophyly of Dendrochirotida was not supported and the group may be paraphyletic. A randomization test using Wills' gap excess ratio found significant congruence between the phylogeny and the stratigraphic record of fossil members, suggesting that the fossil record of holothuroids is not as incomplete as is often stated. The fossil-calibrated tree indicated that several groups of holothuroids survived the end-Permian mass extinction and that the clade composed of Dendrochirotida, Dactylochirotida, Aspidochirotida and Molpadiida rapidly radiated during the Triassic.     

Studies of the fissiparous holothurian Holothuria parvula (Selenka) (Echinodermata: Holothuroidea)

A Bermudan population of the fissiparous holothurian Holothuria parvula (Selenka) was sampled over a 13-month period (1984–1985). Fission was most frequent in the summer when water temperatures were > 25 °C. During fission, the holothurian split into roughly equal parts, and there was little difference in survival of the oral and anal ends. Regeneration of a new gut is a priority and feeding was possible within 2 months of fission. The majority of growth following fission occurred between April and July, just prior to the peak occurrence of fission. Many individuals were fully regenerated within a year, so fission is possibly an annual event. Individuals showing evidence of multiple fission were found. The capacity for sexual reproduction was limited and it appeared to occur mainly during the summer, which was also the peak period for asexual reproduction. No small (< 18 mm) individuals were ever found suggesting that larval recruitment to this population had not recently been successful. The population has probably been maintained recently by fission.     

The oldest synallactid sea cucumber (Echinodermata: Holothuroidea: Aspidochirotida)

Aspidochirote holothurian ossicles were discovered in Upper Ordovician-aged Öjlemyr cherts from Gotland, Sweden. The well-preserved material allows definitive assignment to the family Synallactidae, a deep-sea sea cucumber group that is distributed worldwide today. The new taxon Tribrachiodemas ordovicicus gen. et sp. nov. is described, representing the oldest member of the Aspidochirotida. The further fossil record of Synallactidae and evolutionary implications are also discussed.     

The nonfeeding auricularia of Holothuria mexicana (Echinodermata,Holothuroidea)

Among echinoderms, nonfeeding larvae usually are simplified in body shape, have uniform ciliation, and have lost the larval gut. A few species have nonfeeding larvae that express some remnant features of feeding larvae like ciliated bands and larval skeleton or larval arms, but typically their larval mouth never opens and their gut does not function. Still other species have retained the feeding larval form, a functional gut, and can feed, but they do not require food to metamorphose. The present note describes the development of a tropical holothurian, Holothuria mexicana, which hatches as a gastrula that is already generating coelomic structures. A translucent auricularia forms with a mouth that opens but becomes reduced soon thereafter. In form and ciliation this auricularia resembles a feeding larva, but it does not respond to food. A doliolaria forms on day 4 and the pentactula on day 6 post‐fertilization. Further study of this larva and that of its closely related congener, Holothuria floridana, is warranted.     

Development and morphology of ciliary urns in the sea cucumber Synaptula hydriformis (Echinodermata: Holothuroidea)

Sea cucumbers (holothuroids) lack the only known echinoderm immune organ, the axial organ. Holothuroids of the families Synaptidae and Chiridotidae have coelomic organs, known as ciliary urns, that gather and excrete waste and, therefore, might function in immunity. Although ciliary urns are widely reported and illustrated in the literature, the process and histology of urn development remain unknown. Development and structure of ciliary urns were examined in Synaptula hydriformis using scanning electron, brightfield, and scanning laser confocal microscopy. Mature urns occurred on all three mesenteries in 10‐tentacled young and later growth stages, and developing urns were found in post‐pentactulae, 10‐tentacled young, and released juveniles. Developing urns were circular clusters of ciliated collar cells protruding from the mesentery. The cells increased in number to form the sessile cushion stage with a shallow lumen. The subsequent spoon‐shaped stage had a stalk and a deepened lumen with an extensive ciliary field where coelomocytes began to accumulate. Mature urns had a thin stalk and cornucopia‐shaped body with an abluminal epithelium of squamous cells and an adluminal epithelium of densely packed ciliated collar cells. Cell boundaries of the rim of mature urns and of the stalk and body of developing urns were outlined on one or both sides by microvilli and an elevated cell membrane. Ciliary urns resembling the cushion‐stage urns of S. hydriformis have been described in the sea star Archaster typicus. If urns in these groups are homologous, it is likely that cushion urns are plesiomorphic and that they are present and have been overlooked in other echinoderms.     

Brooding in Psolus patagonicus (Echinodermata: Holothuroidea) from Argentina, SW Atlantic Ocean

The mode, season, and time of brooding, egg diameter, egg number per brood, and the characteristics of newly released juveniles of Psolus patagonicus were investigated off Mar del Plata, Buenos Aires, Argentina, between October 1999 and February 2001. Individuals were attached to the Patagonian scallop, Zygochlamys patagonica. Spawning occurs between February and March. The mean egg diameter, 887 ± 26 μm, is the highest reported for the family Psolidae. Eggs are brooded under the mother’s sole until they develop into crawling juveniles within 7 months. The largest embryos reached a length of 1,941 ± 228 μm in September. During the brooding period (February–September) the number of brooded embryos decreased while their size increased. Our study confirms brooding behaviour in female P. patagonicus.     

Identification of Hox Gene Sequences in the Sea Cucumber Holothuria glaberrima Selenka (Holothuroidea: Echinodermata)

The Echinodermata is a unique animal group forming an early branch in the deuterostomes phylogenetic tree. In echinoids and asteroids a single Hox cluster with nine cognates of the vertebrate Hox paralogous groups has been reported, but no data are available from other echinoderm classes. We report here nine Hox-type sequences from the sea cucumber Holothuria glaberrima, a member of the class Holothuroidea. Partial homeodomain sequences were amplified by polymerase chain reaction from genomic DNA and from a regenerating gastrointestinal tract complementary DNA library. Sequence analyses suggest that the holothuroid cluster has at least three genes of the anterior, one of the medial, and five of the posterior groups. This is the first evidence of five posterior sequences in echinoderms. Received July 19, 1999; accepted October 18, 1999.     

Fine structure of the spermatozoon of the sea cucumber,Leptosynapta clarki (Echinodermata: Holothuroidea)

Summary The spermatozoon of the holothurian Leptosynapta clarki has a small circular head measuring about 3.0 at the greatest diameter, a midpiece containing a single mitochondrion and a tail flagellum measuring between 35 and 45 in length. The acrosomal region contains a granule measuring 0.7 in diameter which consists of electron dense material arranged in concentric lamellae. Five concentric very electron dense lamellae alternate with areas of much less electron dense material in the central region of the granule. This granule rests in an anterior nuclear depression.The nucleus is circular in shape and contains one or two unbound vacuoles which frequently contain a fine granular material. Posteriorly the nucleus is bounded by a large mitochondrion and an occasional Golgi complex. The proximal centriole which contains a lateral arm of dense material lies in a deep fossa projecting into the nucleus. The distal centriole lies posteriorly in the mitochondrial mass and gives rise to nine satellite projections and their Y-shaped connective extensions.The tail contains the 9 + 2 tubule arrangement and tapers at its distal end.This investigation was supported by a National Research Council grant to F. S. Chia.     

Neuroanatomy of the tube feet and tentacles in Holothuria glaberrima (Holothuroidea, Echinodermata)

Echinoderms are a key group in understanding the evolution of the nervous system in the Metazoa. Remarkably, little is known about echinoderm neurobiology. The echinoderm podia, which are unique echinoderm modifications and comprise structures responsible for locomotion and feeding, have been largely neglected in nervous system studies. Here, we have applied immunohistological approaches using different neuronal markers to describe the neuroanatomy of the holothurian podia and its relation to the muscular component. We show, using the sea cucumber Holothuria glaberrima (Selenka, 1867), the direct innervation of the podia by the ectoneural component of the nervous system, as well as the existence of a connection between the nervous system components in the main nerves, the muscle, and the connective tissue. These findings confirm the ectoneural origin of the tube feet’s main nervous system and demonstrate its neuroanatomic complexity. We also show the presence of fibers and neurons within the tube feet mesothelium and connective tissue. The study of these simple structures will help us elucidate the echinoderms’ neuromuscular circuit and their evolutionary relationships.     

Effects of evisceration on oxygen consumption by Stichopus parvimensis Clark (Echinodermata: Holothuroidea)

Near Santa Barbara, California, autotomy of the principal viscera (evisceration) by the holothurian Stichopus parvimensis Clark occurs during October and November, but not during the remainder of the year. The loss of both respiratory trees significantly affects neither the pattern nor magnitude of oxygen consumption relative to that of intact animals. Intact S. parvimensis regulate oxygen consumption over the range of oxygen tensions from P₀₂ = 50 mm Hg to air saturation, while animals without viscera are independent of oxygen tension above a P₀₂ of 75 mm Hg.     

Optimum fishing strategies for Isostichopusfuscus (Echinodermata: Holothuroidea) in the Gulf Of California, Mexico

The Isostichopus fuscus fishery in Mexico was heavily exploited until 1994, when it was closed due to overfishing. However, no information existed on the status of the populations. The fishery was evaluated through an age structured simulation model, and according to our analysis of the stock, the fishery can be feasible and sustainable as long as fishing mortality and age of first catch are optimized. In order to evaluate exploitation strategies, several scenarios were simulated considering different combinations of fishing intensities and ages of first catch. Input data for the model included population parameters, commercial catch and costs and benefits of the fishing operations. Yield production was strongly influenced by the fishing pressure and by the age of first capture. When the first one increased, significant decreases in yield and profits occurred. The best exploitation strategy was these parameters: fishing mortality level F = 0.15, age at first capture t(c) = 4 years, and yielding of approximately 430 tons. However, since the species reproduces for the first time at 5 years, extracting younger specimens would collapse the population. The critical value of fishing mortality was detected at Fc = 0.25. If exceeded, the population tends to exhaustion and the fishery is no longer profitable. In conclusion, I. fuscus fishery is highly vulnerable to overfishing and age of catch. It must be taken into account that the management policies should be considered as pilot and used on a regional basis. Continuous monitoring of the stock, control of the number of fishing licenses and extracting only specimens 5 yeasr-old and older (around 20 cm and >400 g), will allow the populations to recover from fishing activities. Rev. Biol. Trop.     

夏眠对刺参(Apostichopus japonicus (Selenka))能量收支的影响

夏眠是刺参最重要的生理特征;水温升高是其夏眠的主要诱发因子,而夏眠的临界温度与刺参体重密切相关。为揭示刺参夏眠对其能量利用对策的影响,测定了2种体重规格(134.0±13.5)g和(73.6±2.2)g刺参在10、15、20、25℃和30℃5个温度梯度下的能量收支。结果表明,温度和体重及其交互作用对刺参能量的摄入均有显著影响;而温度是影响其摄食能分配的主要因素。研究发现,刺参在非夏眠期、夏眠临界期和完全夏眠期的能量利用对策有所不同:在非夏眠期,刺参摄食能支出的最大组分是粪便能,占摄食能的比例超过50%,其次为呼吸耗能,占19.8%～39.4%,而生长能和排泄能占的比例较小,分别为5.7%～10.7%和2.9%～3.7%;在夏眠临界温度下,呼吸和排泄耗能占摄食能的比例均显著增大(分别为88.3%和13.6%),而生长能所占比例降为负值(-55.3%),刺参表现为负生长;而在夏眠期,刺参的摄食能和排粪能为零,为维持其基本生理活动,不得不动用以往贮存于体内的能量,消耗于呼吸和排泄等生理过程,供维持生命之用。总之,从能量生物学的角度看,夏眠的主要生态学意义在于刺参长时间处于相对高温环境,进而导致摄食受阻条件下的一种能量节约方式。     

Catalogue of neritic-benthonic echinoderms (Echinodermata: Crinoidea, Echinoidea, Holothuroidea) from the Cuban Archipelago

This is an updated taxonomic catalogue of neritic-benthonic Echinodermata (Crinoidea, Echinoidea, Holothuroidea) from Cuba, that includes locality, range, habitat and depth where each species is found. The species list is based on the collections of the Oceanology Institute; Havana, and the "Felipe Poey" Museum (Havana University) Specimens for those collections were captured by a variety of field techniques, narcotized with Cloral hydrate, fixed in formalin and stored in 70-80% alcohol. A total of 53 species were recorded (eight Crinoids, 22 Echinoids and 23 Holothuroids), in 37 genera, 19 families and 12 orders. Ocnus suspectus (Ludwig, 1874) and Phyllophorus (Urodemella) occidentalis (Ludwig, 1885) are new records for Cuban waters.     

The fine structure of the buccal tentacles of Holothuria forskali (Echinodermata,Holothuroidea)

Summary Ultrastructural study of the buccal tentacles of Holothuria forskali revealed that each tentacle bears numerous apical papillae. Each papilla consists of several differentiated sensory buds.The epidermis of the buds is composed of three cell types, i.e. mucus cells, ciliated cells, and glandular vesicular cells (GV cells). The GV cells have apical microvilli; they contain bundles of cross striated fibrillae associated with microtubules. Ciliated cells have a short non-motile cilium. Bud epidermal cells intimately contact an epineural nervous plate which is located slightly above the basement membrane of the epidermis. The epineural plate of each bud connects with the hyponeural nerve plexus of the tentacle. This nerve plexus consists of an axonic meshwork surrounded in places by sheath cells. The buccal tentacles have well-developed mesothelial muscles. Direct innervation of these muscles by the hyponeural nerve plexus was not seen.It is suggested that the buccal tentacles of H. forskali are sensory organs. They would recognize the organically richest areas of the sediment surface through the chemosensitive abilities of their apical buds. Tentacles presumably trap particles by wedging them between their buds and papillae.